Manufacture of gun barrels



United States Patent '0 2,876,095 MANUFACTURE OF GUN BARRELS assignor to Republic Steel Corporation, Cleveland, Ohio, New Jersey No Drawing. Application August 13, 1953 Serial No. 374,131

2 Claims. (Cl. 75-426) This invention relates to the manufacture of gun barrels and the like, and particularly to the production of such articles of steel, and of such character that markedly longer life is obtained.

A frequent problem in gun barrels has been erosion or corrosion of the interior of the barrel, such problem becoming particularly acute in the case of certain types of machine guns and similar pieces as firing rates have increased. For instance, as the firing speed of such devices (e. g. in aircraft) has been raised from 600 rounds per minute to 1200 and now up to materially higher rates, the interior deterioration of the barrel becomes increasingly rapid. Even with short bursts of firing the effects of erosion and corrosion are greatly intensified at the extremely high temperatures reached, the corrosion being occasioned by the gases resulting from explosion of the propellent powder and the erosion probably by gas or solid particles, or both, at the same time.- While extremely hard steels of high temperature resistance may presumably be employed to mitigate this trouble, the difficulty in machining such alloys makes them very expensive, especially for large scale production. Another attempt at solution of the problem, i. e. to avoid the necessity of discarding and replacing gun barrels after only very short total periods of use, has been to employ a stellite liner for some distance of the barrel at the breech end. This expedient has failed to afford a wholly satisfactory solution; the stellite liner is relatively expensive even for the breech locality and is not feasible for the entire barrel, i. e. for the remainder of the barrel, where deterioration may occur at extremely rapid rates of fire.

Accordingly an important object of the present invention is to provide gun barrels and the like of improved composition and characteristics, being composed of steel having other properties (including machineability) suitable for gun barrel manufacture in an eflicient manner, and having at the same time an unusually high resistance to erosion and corrosion, e. g. under high temperature conditions. A further object is to provide procedure for the manufacture of such gun barrels or the metal of which they are made, so as to obtain, in a simple and relatively etficient manner, a metal product having the desired ability to withstand deterioration by the conditions of explosion, corrosive gas and high temperature, such as may occur at the interior surface of a gun barrel.

A further specific object is to afford improved barrels for high speed fire automatic rifles, machine-guns or cannon, and to provide steel from which such barrels may be manufactured, having longer life in ultimate use of the gun, especially by virtue of greater resistance to chemical and physical attack. Further objects are to provide a new procedure for making such articles, as well as to provide improved gun barrels of other character, and likewise other products, having steel compositions of the kind described below and having better 2,876,095 Patented Mar. 3, 1959 stated.

To these and other ends, the invention involves the manufacture of the described articles of specific kinds of steel as will be defined, preferred examples being constructional-type alloy steels having high strength in various respects and other properties particularly suitable for gun barrels. Thus the contemplated compositions are not basically heat resisting or stainless steels; the latter are not feasible to use, even though they might have some inherent advantages of durability. The alloy steels employed for the present invention are likewise to be distinguished from numerous special ferrous alloys (containing high proportions of alloying ingredients), as well as from many ordinary carbon steels and other steel of very low carbon content. In the use of the selected steels (as defined below) for making gun barrels, e. g. by rolling, forging'or other hot working (by deformation) and by ultimate machining, no particular manufacturing problems are encountered, i. e. whether such steel is made with or without the benefit of this invention; nor has it heretofore been apparent that for the described fabrication of gun barrels there was need for any special purification or like treatment, i. e. beyond the conventional deoxidation by addition of usual substances for that purpose, such as manganese, silicon, calcium-silicon.

In other words, the steel compositions specified below are unusually and particularly suitable for manufacture of gun barrels and the like, the purpose of the present invention being by way of improvement, viz. to reduce or delay the erosion and corrosion of the interior of the gun barrel. The interior temperatures reached in use of such articles may easily reach 1300 to 1500" F., and at such temperatures, with the chemical and physical effects of the powder flame and gases, and presumably also solid particles, rapid deterioration of the bore is apt to occur, damaging the rifling and other desired characteristics. These difficulties, as stated, multiply rapidly with increasing rates of fire.

In accordance with the present invention it has now been found that substantial increase of the interior barrel life may be obtained with steels of the defined nature, by incorporating in the molten steel (e. g. in addition to its treatment with the usual deoxidizers) a small quantity, say from 1 to 8 pounds per ton, of a rare earth metal composition, presently preferred examples of such composition comprising cerium, lanthanum, and usually other metals of this group. The rare earth addition is made to the molten metal, either in the ladle which receives the metal from the open hearth or electric furnace, or in the ingot mold as the metal is run into it. The actual nature or mode of operation of the rare earth material in modifying the steel or its properties has not been ascertained, but the resulting metal has been found to possess a remarkably improved resistance to erosion or corrosion (or both) in the guns, e. g. an improve ment in interior barrel life of the order of 15 to 20% and upward even under the extremely severe conditions of aircraft machine-guns firing at materially accelerated rates of fire.

Referring more specifically to the steel compositions utilized in the invention, ithas been explained that these are alloy steels having inherently good characteristics of strength, workability and machineability for use in making gun barrels, and in fact generally comprise compositions that have been employed for such purpose. They are not alloys which are generally spoken of as having high heat resistance, nor are they alloys which in their primary crystalline state have a large crystal size that would tend to impair the life of the alloy in respect to its retention of desirable physical characteristics under high temperature conditions. That is to say, the compositions to which the present invention is applied are readily rolled or otherwise worked and machined, and inherently present no problem of large grains or crystals that might interfere with workability or hot life. These alloys can be defined as consisting of a plurality of the following elements, or as consisting of such elements (of which some may be present in zero or insignificant amount), each within the stated limits of percentage, the balance of the alloy being iron in every case (all percentages here and elsewhere being percentages by weight of the complete composition).

The upper limit of carbon may be alternatively and indeed more precisely defined as the eutectoid point, i. e. in that above this point nodulizing of carbon is apt to occur. It will be understood that this upper point of permissible carbon content may vary somewhat with different compositions in a manner well known and readily recognized in the art; for instance in some compositions the limit may be as low as 0.70% carbon. It will also be understood that in all cases there may be residual or trace amounts of other elements not listed above, of which a primary example is copper that may even .be present up to 0.35% in some cases, although ordinarily for other elements than those specifically listed, the allowable or practical content may be not more than a few hundredths of a percent of each. It will thus be appreciated that the compositions recited and claimed herein as consisting of elements as noted above may also include very small amounts of unavoidable impurities as just explained, in accordance with standard practice in the art. Indeed in compositions embraced by the foregoing table phosphorus and sulfur are usually considered as impurities rather than as specified or required ingredients, the same also applying in a number of individual cases to one or more of the other elements listed.

For complete definition of the alloys, however, the outline presented in Table I must be taken with the further specification that the alloy contains at least one of the alloying metals named, and very preferably in many cases at least two such alloying metals. The components (other than iron and carbon) which are intentionally made to be present in alloy steels for their contribution to the characteristics of the product, are usually designated as specified or required elements, and for convenience such designation will be utilized herein. Thus as stated, the alloy should contain at least one, and usually a plurality of specified or required elements selected from the folloying group, each such element, when required, being present in at least the percentage named with it:

Percent Manganese 0.30 or more Silicon 0.10 or more Chromium 0.10 or more Molybdenum 0.05 or more Vanadium 0.02 or more For many purposes, the alloys do not contain more than a tolerated non-required amount of nickel, say not more than 0.25%, but alternatively in some special cases, e. g. as in making barrels for large guns or cannon, nickel may be advantageous in amounts up to 2% and more.

While the upper range of sulfur is indicated in Table I as 0.10% in that it may reach this figure for a high sulfur, highly machineable steel, the upper limit of sulfur for articles such as high speed aircraft gun barrels is 0.075% the. actual sulfur content being preferably kept at not more than about 0.04% in such cases.

Certain preferred compositions to which the invention is specifically applicable with unusual advantage are those wherein the silicon content is not more than about 0.50% and the manganese not more than about 1.10%. Likewise the chromium content may usually be kept at not more than about 1.25% or so, although higher percentages (within the range of Table I) can ordinarily be tolerated. On the other hand, with respect to the upper limits of Table I on manganese and silicon, it is contemplated that the advantage of the invention can be realized, and that articles of the character stated can be produced for some purposes, with so-called silicon-man ganese steels (which are more of the nature of a spring steel, e. g. wherein the silicon content may range from 1.80 to 2.20%.

In the following table, there are set forth two specific types of steels, defined by ranges of analysis of the component elements in percentage, with which the invention has been very successfully practiced and which are particularly suitable for barrels of machine guns and the like, these two types of composition being respectively designated as A (a chromium-molybdenum-vanadium alloy) and B (a chromium-molybdenum alloy):

Table 11 Element.

Vanadium A typical composition of a considerably different alloy In carrying out the invention with respect to the treatment of the steel, the latter is made in the usual way, e. g. in an open hearth or electric furnace. Alloying or other additions are effected with respect to the metal in the furnace, or in the ladle (as or after the molten composition from the furnace is poured into it), in accordance with standard practice. Thus, for instance, with compositions of the type specified in Table II above, some alloysuitable deoxidizer for the compositions of Table II is a calcium-manganese-silicon alloy (with no aluminum) of conventional composition for such purpose.

The steel is thus produced and discharged from the open hearth or electric furnace into the ladle, and likewise poured from the ladle into molds (e. g. conventional ingot molds), all in the customary fashion. Pursuant to the present invention, the rare earth metal composition is added to the molten metal after its discharge from the furnace and prior to the solidification of the metal in the mold. Thus the addition can be effected either in the ladle or in the mold itself, but in the latter case, preferably during or promptly after pouring and well before substantial solidification has occurred. In order to avoid wasteful consumption of the rare earths for ordinary deoxidizing effect, i. e. for the function normally performed by the deoxidizing agents as mentioned above, it is desirable to add the rare earths after deoxidizers have been added or at least with or not long prior to the addition of such materials. At least for manipulative convenience, it appears somewhat preferable to add the rare earths to the ladle, e. g. by simply dropping the material into the ladle after a small amount of metal has accumulated in it, the remainder of the steel then being poured in. On the other hand, if the rare earth mixture is added to the molds, one way is to drop in successive pieces of the mixture as the mold fills.

The rare earth metal material which is thus incorporated in the molten steel may be added conveniently either in the metallic state or in the state of oxides of the specified rare earth metals, or indeed as a mixture of metals and oxides. It will therefore be understood that herein and in the appended claims, references to rare earth metals and rare earth metal mixtures should be taken to include oxides as well as the elements in metallic form, i. e. unless the contrary appears as by direct reference to the metallic condition. In all cases, amounts of the rare earth addition are expressed as if in weight of the elements in metallic state; thus each reference to a specified amount of rare earth metal mixture means the amount of rare earth elements themselves (rather than total amount, for example, of oxides) even when such are added in the compound form.

As indicated above, the rare earth addition is of a mixture of rare earth metals, preferably one or another of the types of mixture commercially produced and sold under various names or trade names, e. g. presumably as the result of reduction of rare earth metal ores without extraordinary attempt to segregate individual elements of this group from each other. In a type of rare earth mixture which has been satisfactorily employed to achieve the stated results (in improvement of gun barrel life), at least the major part (i. e. more than half) of the mixture has consisted of cerium and lanthanum, cerium also representing much more than half of the total of these two elements. The balance of the rare earth material understood to be found in commercially available mixtures of this type comprises one or more, often a plurality of other rare earth metals such as neodymium, praseodymium, terbium, yttrium and samarium; in certain specific preparations suitable for the present process, neodymium is usually a chief minor ingredient, i. e. among the components other than cerium and lanthanum. Stated in another way, a useful type composition (according to tests) is a mixture of rare earths, wherein the element cerium is the component of largest amount (say from 40 to 75% and most of the balance is lanthanum and one or more other rare earth elements (usually at least including neodymium and praseodymium), with lanthanum in amount at least about equal to any one of such others.

One specific composition of rare earths which has been employed with particular success is a mixture sold commercially under the name Lanceramp and having a com position stated to be as follows: 50% cerium, 20% lanthanum, 18% neodymium and praseodymium,

perhaps very minor amounts of other rare earths and impurities. Alternatively rare earth mixtures of the type which in their metallic state are known as mischmetal or cerium-mischmetal, can be used. A typical composition of commercial rnischmetal is 50-55% cerium, 22-25% lanthanum, 15-17% neodymium, 8 to 10% of a mixture of four or five other rare earths (e. g. specifically as named above) and 0.5-3% iron.

As stated, the rare earth addition is made to the molten steel, improved results being noted where the addition is in the range of one to six pounds of the rare earth metal mixture per ton of steel. Particularly definite advantage is apparent where the addition is of at least two pounds per ton, preferred practice being to use about four pounds per ton of a material such as the Lanceramp composition noted above. Electric furnace steel seems to require somewhat more rare earth metal addition (to provide the same effect) than open hearth steel, although in all cases the addition may be within the ranges herein generally stated. As a rule, six pounds of the rare earth mixture is about the most that is needed for good realization of the desired effects. However, no objection has been found to the addition of greater amounts, e. g. up to ten pounds per ton, except as usually representing an unnecessary and uneconomical excess in view of the cost of the rare earth material.

Following the rare earth addition to the molten steel, the further treatment of the latter and the operations for fabrication of gun barrels may follow conventional practice, i. e. including rolling or other hot working (e. g. forging or other working by deformation) to provide blanks or rough blanks, the finished barrels being customarily achieved by machining operations. Aside from maintaining the molten condition of the steel for good distribution of the rare earth material in the molten mass, there appears to be no long time factor involved in the treatment; thus the addition of the rare earth to the molten metal in the ingot molds as or soon after the latter are poured seems to provide full achievement of the desired effects, without prolonging or interrupting the normal course of handling of the molds and of solidification of the metal in them.

By way of more specific example, one of a number of batches of steel in and with which the present improvements have been successfully performed, constituted an alloy steel which was in the category of composition A above and which after all furnace, ladle and mold additions (including additions conventional in regular gun barrel practice, as well as the addition of rare earths) had the following analysis.

The steel was made in an open hearth furnace and conventional furnace additions of molybdenum, silicon, manganese and chromium were effected for this heat, and likewise ladle additions of manganese, vanadium, coal and deoxidizer, the latter being calcium-manganese-silicon alloy added in the amount of 1200 pounds to a ladle containing approximately tons. In one of the ingots poured from the ladle (at about 2800 F.) the above described Lanceramp alloy (in metallic state) was added in a quantity of four pounds per ton of steel, e. g. 23 pounds of the mixture in an ingot mold filled to contain 5% tons. The rare earth was incorporated by inserting several successive pieces of the Lanceramp alloy as the with mold was filled. Subsequent treatment of the steel and subsequent fabrication were in accordance with conventional practice, especially for gun barrel manufacture; the filled molds were held in pits for the usual time of two hours or so and the metal subsequently stripped from the molds was then subjected to customary blooming and rolling operations. Pieces suitable for gun making were ultimately produced and gun barrels made from them as well as from other portions of the same open hearth furnace heat, to which no rare earth addition has been made. Tests of pieces of the two batches of steel, i. e. made with and without the rear earth addition, showed no significant difference in physical properties, i. e. as to tensile strength, hardness, hardenability, cleanliness, general quality and grain size. However, tests of machine gun barrels made of the steel which had received the rare earth addition were found to have markedly improved properties (over those made without the addition), e. g. to have a substantially longer firing life (at least 20%) before having to be discarded because of erosion or corrosion in the bore.

As indicated above, the chemical and physical mechanism whereby the rare earth addition effects the described improvements in the gun barrels has not been ascertained, nor is there any convenient way of determining the precise nature of the effect. Appropriate examinations, however, tend to indicate that the result is not simply an ordinary deoxidation effect, nor is it related to any reduction of grain or crystal size, or indeed any other property heretofore understood to be affected by the use of rare earth metals in other types of ferrous metal compositions. That is to say, no significant difference in corresponding properties was detectable, between the steel made with and without the rare earth addition. Analysis of the rare earth-treated product for content of all the various rare earth metals actually employed is practically impossible. In the rare earth-treated ingot of the specific example above, it was found that the ultimate solid steel had a cerium content of about 0.038%, such result representing a survival of about 40% of the cerium which was introduced as a component of the rare earth metal mixture. It thus cannot necessarily be said that detectable presence of rare earth metals in the ultimate steel, or in the material of the gun barrel itself, is necessary; indeed the treatment may be entirely effective even though its function or the nature of the steel-producing and handling operation may be such as to destroy much or perhaps all of the rare earth addition. Nevertheless the effect of such addition, particularly in providing the described improvement in gun barrel life is entirely definite and detectable as such, demonstrating the production of an article having unquestionably new properties, specifically a higher resistance to the dcteriorating influence occurring in the bore of the gun as the latter is used.

It is to be understood that the invention is not limited to the specific embodiments herein set forth but may be carried out in other ways without departure from its spirit.

8 I claim: 1. A steel gun barrel composed of alloy steel which consists of iron and other substances as follows, in percentage by weight:

Carbon 0.40-0.50 Manganese 0.40-0.90 Phosphorus 0.040 max. Sulfur 0.040 max. Silicon 0.15-0.35 Chromium 0.80-1.15 Molybdenum 0.30-0.40 Vanadium 0.20-0.35

said steel having been produced by procedure which includes, after discharge of the molten steel from the furnace in which it is made, the addition to the molten steel of a rare earth metal mixture in amount of 1 to 6 pounds per ton of steel, said rare earth metal mixture comprising at least in major part cerium and lanthanum, said gun barrel having resistance to internal deterioration in firing, and said deterioration resistance being produced by said addition of rare earth metal mixture to the steel and being substantially greater than in a gun barrel of like steel produced without said addition of rare earth metal mixture.

2. A steel gun barrel composed of alloy steel which consists of iron and other substances as follows, in percentage by weight:

Carbon 0.45-0.60 Manganese 0.60-1.00 Phosphorus 0.040 max. Sulfur 0.040 max. Silicon 0.20-0.35 Chromium 0.80-1.15 Molybdenum 0.08-0.25

said steel having been produced by procedure which includes, after discharge of the molten steel from the furnace in which it is made, the addition to the molten steel of a rare earth metal mixture in amount of 1 to 6 pounds per ton of steel, said rare earth metal mixture comprising at least in major part cerium and lanthanum, said gun barrel having resistance to internal deterioration in firing, and said deterioration resistance being produced by said addition of rare earth metal mixture to the steel and being substantially greater than in a gun barrel of like steel produced without said addition of rare earth metal mixture.

References Cited in the file of this patent UNITED STATES PATENTS Tisdale et a1 June 30, 1953 Tisdale et al. July 13, 1954 OTHER REFERENCES 

1. A STEEL GUN BARREL COMPOSED OF ALLOY STEEL WHICH CONSISTS OF IRON AND OTHER SUBSTANCES AS FOLLOWS, IN PERCENTAGE BY WEIGHT: 